My U.S. Pat. No. 6,555,931 describes renewable energy systems of a non-turbine variety using long-stroke reciprocating motion of one or more tethers each attached to an element extracting useful energy from naturally occurring fluid flow of air (wind) or water (currents or tides). U.S. Pat. No. 6,555,931 is incorporated by reference herein.
Wind turbines are being deployed at a rapid pace both on land and off-shore. Land use, push-back by local populace, land cost, and site-specific avian mortality problems have limited terrestrial development of wind farms. This has spurred interest in developing large off-shore wind farms. In shallow areas, turbine towers are attached to the seabed, but the interest in less congested and more remote deep-water areas increases as close off-shore shallow venues have also come under attack.
Regarding very large deep-water off-shore wind energy development, economies of scale point to ever increasing turbine size making the installation and very logistics of transporting tower and blade sections problematic. With turbine-tip speed limits and even taller structures to contend with, it is interesting that using oil platform technology or counter-weighted ocean floor tethered floating platforms are considered (by some) to be both cost-effective and practical.
Actually, large reciprocating wind energy systems may be more compatible with the task at hand. The main attraction for deep-water use is the elimination of the tower structure with its attendant turning moment transmitted to the supporting structure. The installation would be at sea-level since only airfoils would be aloft. A floating platform can be totally fitted at dockside and just towed to its deployed area; it can also be moved to shore for any major repairs (or they can be easily and safely performed at sea). Since all components of a reciprocating wind system are modular and relatively small (airfoils can be “folded”), there is no transportation problem. No special vessels with cranes are required for erection, deployment, or maintenance/repairs. There are no known size limitations comparable to those imposed by turbine blade root stress or blade tip speed, so that size can be more easily dictated by economic as opposed to technology considerations.
However, there are some problems in scaling up power drums, capstan, or windlass type tether handling devices for long-stroke systems that would be handling tethers of several inches diameter and under extremely high tension. These devices are used to convert the linear tether motion into more useful rotary motion. If very large diameters are used, rotary speed will be slow thereby increasing the cost of transmission components. If strokes are limited to mitigate this problem, system efficiency suffers.